I just tried to use the laboratory books and boy, it did not end well.

There seems to be a problem with \experiment, as I get a bunch of errors whenever I include it. Most of them are rather generic and probably errors thrown because of some main error , except for this one:

Paragraph ended before \fk@@getatdashsep@list was complete.

Other commands from the custom labbook class, like \labday work perfectly fine.On CTAN someone commented that the package broke with TEXLive-2018. :<

I hope someone with more knowledge about document classes can help to fix it, as I don't know what to try

Thank you for letting us know the solution you found. Yes, it's due to a change in the new LaTeX kernel that utf8 is now used by default as the input encoding. That came with TeX Live 2018, but would happen with MiKTeX at some version as well. That labbook class has an ANSI encoded § though, so it breaks. It should never happen that a class uses non-ASCII characters because it requires a specific encoding and can break in any other encoding. I hope the class author will fix it at some time.

Though \UseRawInputEncoding fixes the issue, I hope you won't encounter another encoding issue as consequence.

Thanks for posting about this! Unfortunately I can't be everywhere at once so it's very useful when users report that templates are no longer working after a new release so I can fix things up quickly.